Polyolefins are ubiquitous products in modern society, billions of kilograms being produced yearly. There has been a continuing interest in catalysts that can produce such polymers more cheaply and/or produce polymers with different structures and improved desirable properties. In the last decade or so, it has been found that certain late transition metal complexes can polymerize various olefins, often to form polymers which are difficult or impossible to obtain using other olefin polymerization catalysts.
Among these late transition metal catalysts have been iron and cobalt complexes of diimines of 2,6-pyridinedicarboxaldehydes and 2,6-diacylpyridines, which are especially useful for polymerization or oligomerization of ethylene, see for instance U.S. Pat. Nos. 5,955,555 and 6,103,946 and 6,545,108. It has now been discovered that iron and cobalt complexes of certain tricyclic ligands containing a “pyridine ring” and substituted with two imino groups are catalysts for the polymerization and/or oligomerization of olefins, especially ethylene.